update.sh: Add SPAMHAUS_DROP if SPAMHAUS_EDROP was previously used

update.sh: Add SPAMHAUS_DROP if SPAMHAUS_EDROP was previously used

- I realised that the previous patch for update.sh related to the ipblocklist removal
   of ALIENVAULT and SPAMHAUS_EDROP only removed the SPAMHAUS_EDROP setting. It makes sense
   to add SPAMHAUS_DROP to the settings file if SPAMHAUS_EDROP was previously used and
   SPAMHAUS_DROP was not selected.
- This patch adds the above change.

Tested-by: Adolf Belka <adolf.belka@ipfire.org>
Signed-off-by: Adolf Belka <adolf.belka@ipfire.org>
Signed-off-by: Arne Fitzenreiter <arne_f@ipfire.org>